Hot gas turbine machine have found wide application as jet propulsion engines, for example, as aircraft gas turbines, and as electrical power generation plants. Hot gas turbines utilize combustion of a suitable air/fuel mixture in a combustion chamber as a source for hot gas. This hot gas is then directed from the combustion chamber through airfoil turbine blades or buckets mounted in a circular row on the periphery of a turbine wheel disc. These buckets or blades extract energy from the hot gases passing therebetween and convert some of the noted energy into rotational motion of the turbine wheel. The turbine wheel comprising the turbine disc with a row of blades or buckets on the periphery thereof is usually mounted concentrically within an engine casing or housing, and the hot gases are ducted from the combustion chamber through or between the turbine blades usually by means of a suitable annular chamber or duct which is positioned closely adjacent the peripheral row of the buckets or blades which are attached to the periphery of the turbine disc. The annular duct directs most of the combustion gases to the annular area defined by the row of blades on the turbine disc so that most of the hot gas is caused to flow between the blades in the row on the disc. It is important, for energy extraction purposes, that the hot gases pass through or between the turbine blades and not be directed against the face of the turbine disc. In the latter instance a circular shroud ring member is concentrically mounted in the turbine machine casing around the turbine wheel. The shroud ring member may be described as a short cylindrical or rim member with an arcuate surface which fits very closely to the tips of the blades or buckets on the turbine disc. The use of a closely fitting shroud or rim member at the periphery or tips of the blades of a turbine wheel provides a satisfactory gas seal so that most of the hot gases pass between the blades for efficient energy extraction, and very little is lost by passing over the periphery of the blades.